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  • 1
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    A haplotype-based framework for group-wise transmission/disequilibrium tests for rare variant association analysis (2015)
    Oxford University Press
    Details
    Publication Date: 2015-04-28
    Description: Motivation: A major focus of current sequencing studies for human genetics is to identify rare variants associated with complex diseases. Aside from reduced power of detecting associated rare variants, controlling for population stratification is particularly challenging for rare variants. Transmission/disequilibrium tests (TDT) based on family designs are robust to population stratification and admixture, and therefore provide an effective approach to rare variant association studies to eliminate spurious associations. To increase power of rare variant association analysis, gene-based collapsing methods become standard approaches for analyzing rare variants. Existing methods that extend this strategy to rare variants in families usually combine TDT statistics at individual variants and therefore lack the flexibility of incorporating other genetic models. Results: In this study, we describe a haplotype-based framework for group-wise TDT (gTDT) that is flexible to encompass a variety of genetic models such as additive, dominant and compound heterozygous (CH) (i.e. recessive) models as well as other complex interactions. Unlike existing methods, gTDT constructs haplotypes by transmission when possible and inherently takes into account the linkage disequilibrium among variants. Through extensive simulations we showed that type I error was correctly controlled for rare variants under all models investigated, and this remained true in the presence of population stratification. Under a variety of genetic models, gTDT showed increased power compared with the single marker TDT. Application of gTDT to an autism exome sequencing data of 118 trios identified potentially interesting candidate genes with CH rare variants. Availability and implementation: We implemented gTDT in C++ and the source code and the detailed usage are available on the authors’ website ( https://medschool.vanderbilt.edu/cgg ). Contact: bingshan.li@vanderbilt.edu or wei.chen@chp.edu Supplementary information: Supplementary data are available at Bioinformatics online.
    Print ISSN: 1367-4803
    Electronic ISSN: 1460-2059
    Topics: Biology , Computer Science , Medicine
    Published by Oxford University Press
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  • 2
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    Genetic factors affecting gene transcription and catalytic activity of UDP-glucuronosyltransferases in human liver (2014)
    Oxford University Press
    Details
    Publication Date: 2014-09-20
    Description: The aim of this study was to discover cis - and trans -acting factors significantly affecting mRNA expression and catalytic activity of human hepatic UDP-glucuronosyltransferases (UGTs). Transcription levels of five major hepatic UGT1A ( UGT1A1, UGT1A3, UGT1A4, UGT1A6 and UGT1A9 ) and five UGT2B ( UGT2B4, UGT2B7, UGT2B10, UGT2B15 and UGT2B17 ) genes were quantified in human liver tissue samples ( n = 125) using real-time PCR. Glucuronidation activities of 14 substrates were measured in 47 livers. We genotyped 167 tagSNPs (single-nucleotide polymorphisms) in UGT1A ( n = 43) and UGT2B ( n = 124), as well as the known functional UGT1A1*28 and UGT2B17 CNV (copy number variation) polymorphisms. Transcription levels of 15 transcription factors (TFs) known to regulate these UGTs were quantified. We found that UGT expression and activity were highly variable among the livers (median and range of coefficient of variations: 135%, 74–217% and 52%, 39–105%, respectively). CAR, PXR and ESR1 were found to be the most important trans -regulators of UGT transcription (median and range of correlation coefficients: 46%, 6–58%; 47%, 9–58%; and 52%, 24–75%, respectively). Hepatic UGT activities were mainly determined by UGT gene transcription levels. Twenty-one polymorphisms were significantly (FDR-adjusted P 〈 0.05) associated with mRNA expression and/or activities of UGT1A1 , UGT1A3 and UGT2B17 . We found novel SNPs in the UGT2B17 CNV region accounting for variability in UGT2B17 gene transcription and testosterone glucuronidation rate, in addition to that attributable to the UGT2B17 CNV. Our study discovered novel pharmacogenetic markers and provided detailed insight into the genetic network regulating hepatic UGTs.
    Print ISSN: 0964-6906
    Electronic ISSN: 1460-2083
    Topics: Biology , Medicine
    Published by Oxford University Press
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  • 3
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    Cryo-EM reveals a novel octameric integrase structure for betaretroviral intasome function (2016)
    Nature Publishing Group (NPG)
    Details
    Publication Date: 2016-02-19
    Description: Retroviral integrase catalyses the integration of viral DNA into host target DNA, which is an essential step in the life cycle of all retroviruses. Previous structural characterization of integrase-viral DNA complexes, or intasomes, from the spumavirus prototype foamy virus revealed a functional integrase tetramer, and it is generally believed that intasomes derived from other retroviral genera use tetrameric integrase. However, the intasomes of orthoretroviruses, which include all known pathogenic species, have not been characterized structurally. Here, using single-particle cryo-electron microscopy and X-ray crystallography, we determine an unexpected octameric integrase architecture for the intasome of the betaretrovirus mouse mammary tumour virus. The structure is composed of two core integrase dimers, which interact with the viral DNA ends and structurally mimic the integrase tetramer of prototype foamy virus, and two flanking integrase dimers that engage the core structure via their integrase carboxy-terminal domains. Contrary to the belief that tetrameric integrase components are sufficient to catalyse integration, the flanking integrase dimers were necessary for mouse mammary tumour virus integrase activity. The integrase octamer solves a conundrum for betaretroviruses as well as alpharetroviruses by providing critical carboxy-terminal domains to the intasome core that cannot be provided in cis because of evolutionarily restrictive catalytic core domain-carboxy-terminal domain linker regions. The octameric architecture of the intasome of mouse mammary tumour virus provides new insight into the structural basis of retroviral DNA integration.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Ballandras-Colas, Allison -- Brown, Monica -- Cook, Nicola J -- Dewdney, Tamaria G -- Demeler, Borries -- Cherepanov, Peter -- Lyumkis, Dmitry -- Engelman, Alan N -- 9 P41 GM103310/GM/NIGMS NIH HHS/ -- P30 AI060354/AI/NIAID NIH HHS/ -- P41 GM103331/GM/NIGMS NIH HHS/ -- P50 GM082251/GM/NIGMS NIH HHS/ -- P50 GM103368/GM/NIGMS NIH HHS/ -- R01 AI070042/AI/NIAID NIH HHS/ -- England -- Nature. 2016 Feb 18;530(7590):358-61. doi: 10.1038/nature16955.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Cancer Immunology and Virology, Dana-Farber Cancer Institute and Department of Medicine, Harvard Medical School, 450 Brookline Avenue, Boston, Massachusetts 02215, USA. ; Laboratory of Genetics and Helmsley Center for Genomic Medicine, The Salk Institute for Biological Studies, 10010 N Torrey Pines Road, La Jolla, California 92037, USA. ; Clare Hall Laboratories, The Francis Crick Institute, Blanche Lane, South Mimms, Potters Bar, Hertfordshire EN6 3LD, UK. ; Department of Biochemistry, The University of Texas Health Science Center at San Antonio, 7703 Floyd Curl Drive, San Antonio, Texas 78229, USA. ; Division of Medicine, Imperial College London, St. Mary's Campus, Norfolk Place, London W2 1PG, UK.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/26887496" target="_blank"〉PubMed〈/a〉
    Keywords: Catalytic Domain ; *Cryoelectron Microscopy ; Crystallography, X-Ray ; DNA, Viral/chemistry/*metabolism/*ultrastructure ; Integrases/*chemistry/metabolism/*ultrastructure ; Mammary Tumor Virus, Mouse/chemistry/*enzymology/genetics/ultrastructure ; Models, Molecular ; *Protein Multimerization ; Protein Structure, Quaternary ; Spumavirus/chemistry/enzymology ; Virus Integration
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Published by Nature Publishing Group (NPG)
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  • 4
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    Graţianite, MnBi2S4, a new mineral from the Baia Bihor skarn, Romania (2014)
    Mineralogical Society of America
    Details
    Publication Date: 2014-05-16
    Description: The new mineral graţianite, MnBi 2 S 4 , is described from the Bǎia Bihor skarn deposit, Bihor County, Romania. Graţianite occurs as thin lamellae, intimately intergrown with cosalite and bismuthinite, or as flower-shaped blebs within chalcopyrite, where it is associated with cosalite and tetradymite. Graţianite displays weak to modest bireflectance in air and oil, respectively, and strong anisotropy. The mean empirical composition based on 20 electron probe microanalyses is: (Mn 0.541 Fe 0.319 Pb 0.070 Cu 0.040 Cd 0.009 Ag 0.001 ) S0.980 (Bi 1.975 Sb 0.018 ) S1.993 (S 4.008 Se 0.012 Te 0.007 ) S4.027 , corresponding to the ideal formula MnBi 2 S 4 . Graţianite crystallizes in the monoclinic system (space group C 2/ m ). Single-crystal X-ray studies of material extracted by the focused ion beam-scanning electron microscopy (FIB-SEM) technique, and carried out on the MX2 macromolecular beamline of the Australian Synchrotron determined the following cell dimensions: a = 12.6774(25) Å, b = 3.9140(8) Å, c = 14.7581(30) Å, b = 115.31(3)°, V = 662.0(2) Å 3 , and Z = 4. The six strongest X-ray reflections and their relative intensities are: 3.448 Å (100), 2.731 Å (77), 2.855 Å (64), 3.637 Å (55), 3.644 Å (54), and 3.062 Å (51). Graţianite is the monoclinic analog of berthierite (FeSb 2 S 4 ), garavellite [Fe(Bi,Sb) 2 S 4 ] and clerite [Mn(Sb,As) 2 S 4 ] (Nickel-Strunz class 02.HA.20). It is isostructural with synthetic sulfides and selenides in the MnBi 2 S 4 –MnSb 2 S 4 and MnBi 2 Se 4 –MnSb 2 Se 4 series, and with grumiplucite (HgBi 2 S 4 ) and kudriavite, [(Cd,Pb)Bi 2 S 4 ], 3 P members of the pavonite homologous series. The mineral is named for Graţian Cioflica (1927–2002), formerly Professor in Mineralogy and Ore Deposits at the University of Bucharest, Romania. The Băia Bihor skarn, like others within the same belt, is geochemically complex. The availability of Cu, Zn, and Pb, but also Ag, Bi, Mo, and B, as well as a wide range of minor elements, has created an environment allowing for crystallization of an unusually diverse range of discrete minerals. Graţianite is part of the peculiar associations of Bi–Pb-sulfosalts and Bi-chalcogenides that are genetically related to Au-enrichment. This study demonstrates the versatility of FIB-SEM techniques for in situ extraction of small volumes of well-characterized material, coupled with single-crystal X-ray analysis using synchrotron radiation, for the characterization of new minerals.
    Print ISSN: 0003-004X
    Electronic ISSN: 1945-3027
    Topics: Geosciences
    Published by Mineralogical Society of America
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  • 5
    Electronic Resource
    Electronic Resource
    Thermobarometry of the Bleikvassli Zn-Pb-(Cu) deposit, Nordland, Norway (1998)
    Springer
    Mineralium deposita 34 (1998), S. 19-34 
    Details
    ISSN: 1432-1866
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract The Bleikvassli massive sulfide ore deposit is hosted by Proterozoic pelitic, quartzofeldspathic, and amphibolitic rocks of the Uppermost Allochthon of the Scandinavian Caledonides. Staurolite-garnet-biotite and kyanite-staurolite-biotite assemblages indicate that metamorphism reached the kyanite zone of the amphibolite facies. Geothermobarometry was conducted on rocks in and around the deposit using a variety of silicate and sulfide calibrations. Temperature determinations are most reliant on the garnet-biotite exchange reaction, with analyses obtained from 259 garnet rims and adjacent biotite. Results from nine calibrations of the garnet-biotite geothermometer are considered, but compositional limitations of many calibrations involving high Ca and Mn contents in garnet and AlVI and Ti in biotite make many of the coexisting mineral pairs unsuitable. Average temperatures calculated from the two calibrations that most closely address the garnet-biotite compositions observed at Bleikvassli are 584 °C ± 49 °C and 570 °C ± 40 °C. The application of two calibrations of the garnet-staurolite geothermometer on a limited number of samples yields 581 °C ± 2 °C and 589 °C ± 12 °C, assuming a H2O=0.84, based upon calculations of the modal proportions of gaseous species. Pressure determinations are less constrained. Phengite and plagioclase-biotite-garnet-muscovite geobarometers give average pressures of approximately 5.0 kbar and 8.5 ± 1.2 kbar, respectively. Pressures obtained from the sphalerite-hexagonal pyrrhotite-pyrite barometer average 7.7 ± 1.0 kbar. In consideration of these results, the peak metamorphic conditions at the Bleikvassli deposit are estimated to be 580 °C and 8 kbar.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s001260050183
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  • 6
    Electronic Resource
    Electronic Resource
    Mineralogy and textural relationships among sulphosalts and related minerals in the Bleikvassli Zn-Pb-(Cu) deposit, Nordland, Norway (1998)
    Springer
    Mineralium deposita 34 (1998), S. 35-56 
    Details
    ISSN: 1432-1866
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Several distinct assemblages of Pb-Sb, Pb-As, Cu-Pb-Sb and Cu-Fe-Zn-Sn sulphosalts are identified in sulphide samples from Bleikvassli mine, Norway. Detailed optical microscopy and electron probe microanalysis have permitted investigation of textural relationships between minerals and compositional variations between different ore types. Tetrahedrite, typically containing 10–16 wt.% Ag (rare freibergite containing 25–30 wt.% Ag has also been identified in two samples), stannite (Cu2(Fe〉Zn)SnS4), and meneghinite, CuPb13Sb7S24, are widely distributed as trace constituents throughout massive pyritic and galena-rich ores. Native antimony and pyrargyrite occur in trace amounts in all ore types, as the breakdown products of earlier sulphosalts. Several distinct types of wall-rock mineralisation are present at Bleikvassli. Of considerable mineralogical interest are the coarse-grained sulphide mobilisates within the wall rock which contain a distinct␣and characteristic suite of Pb-As sulphosalts:␣tennantite + jordanite (Pb14As6S23) + seligmannite (CuPbAsS3) ± dufrenoysite (Pb2As2S5). Bournonite (CuPbSbS3) is the only Sb-bearing sulphosalt recognised in significant amounts within the mobilisates, meneghinite and tetrahedrite being conspicuously absent. These mobilisates display considerable Au enrichment; electrum can be confirmed, intimately associated with jordanite and tennantite. Appreciable Sb (up to 3 wt.%) is contained within galena in the mobilisates, in contrast to galena from massive ores which contains only negligible Sb. Contents of Ag and Bi in galena vary considerably in all ore types, but confirm earlier suggestions that galena is a major Ag-carrier at Bleikvassli. Boulangerite (Pb5Sb4S11), jamesonite (FePb4Sb6S14) and gudmundite (FeSbS) occur in trace amounts. Sn-sulphosalts are represented by kësterite, (Cu2(Zn〉 Fe)SnS4), but commonly zoned with respect to Zn/Fe ratio, in the mobilisates, rather than by stannite. A rare type of mobilisate, also in the wall rock, in which chalcocite and bornite are the main minerals, contains native Ag, stromeyerite (AgCuS), mckinstryite ((Ag,Cu)2 S), Ag-free tetrahedrite, an unnamed Cu-Ag-Fe sulphide (Cu3Ag2FeS4) and native Bi, myrmekitically intergrown with chalcocite. Although a comprehensive genetic model for the wall-rock mineralisation at Bleikvassli is largely impossible given the limitations in the present state of knowledge regarding mechanisms involved in remobilisation processes, a multi-stage model of remobilisation during regional metamorphism is considered to best explain the observations. An interplay of different solid- and liquid-state remobilisation mechanisms, in various combinations, is required to account for the macro- and microscopic observations. Remobilisation probably began during the earlier stages of metamorphism, with crystallisation and further remobilisation taking place during the entire metamorphic cycle, giving rise to the extensive chemical and mineralogical diversity observed today. Preserved mineral assemblages and their textural relationships reflect a complex sequence of replacement and decomposition reactions taking place during the latest phase of late-metamorphic crystallisation and subsequent cooling.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s001260050184
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  • 7
    Electronic Resource
    Electronic Resource
    Sphalerite remobilization during multistage hydrothermal mineralization events —examples from siderite-Pb-Zn-Cu-Sb veins, Rheinisches Schiefergebirge, Germany (1998)
    Springer
    Mineralogy and petrology 63 (1998), S. 223-241 
    Details
    ISSN: 1438-1168
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Description / Table of Contents: Zusammenfassung Innerhalb zahlreicher varistischer Siderit-Pb-Zn-Cu-Ganglagerstätten des Rheinischen Schiefergebirges erfolgte eine hydrothermale überprägung durch spätvaristische Sb-reiche Fluide, die entlang der präexistenten tektonischen Elemente der Gänge bevorzugte Wegsamkeiten fanden. In einigen Fällen führte dieses spätere Hydrothermalereignis zu einer bedeutenden Veränderung der Gefüge der primären Sulfidmineralisation. In den Lagerstätten Stahlberg (Müsen), Schöne Freundschaft (Obersdorf) und Silberwiese (Oberlahr) im Siegerland-Wied-Distrikt und Silbersand (Mayen) und Saarsegen (Altenahr) in der östlichen Eifel stellt Sphalerit eine Hauptkomponente der primären Mineralisation dar. Die Gefüge des primären Sphalerit (Sphalerit I) zeigen eine sukzessive Entwicklung, die von Korrosion und partieller Verdrängung durch verschiedene Pb-Sb-Sulfosalze über intensive Wiederauflösung schließlich zu vollständiger Remobilisation führt. Remobilisierter Sphalerit wurde teilweise wieder als jüngere Generation (Sphalerit II) abgeschieden. Eine vergleichbare Gefügeentwicklung liegt in Proben der Dörnberg-Aurora-Lagerstätte (Ramsbeck) vor, obwohl hier verschiedene überprägungsstadien und wiederholte Remobilisationen von Sphalerit während einer komplexeren tektonischen und hydrothermalen Entwicklung erfolgten. Mikrosondenanalysen von Sphalerit aus verschiedenen texturellen Stadien zunehmender Korrosion und Verdrängung belegen eine intensive diffusive Verarmung an Fe in einer Zone parallel zur Verdrängungsfront. Sphalerit der jüngeren Generation hat demgegenüber sehr geringe Gehalte an Fe. Die Analysendaten zeigen weitgehende übereinstimmung mit theoretischen überlegungen und experimentellen Ergebnissen zur Interdiffusion von Fe und Zn in Sphalerit, der im Kontakt mit einem Fluid mit niedrigem Fe/Zn-Verhältnis steht. Die Wechselwirkung mit den hochtemperierten Sbreichen Fluiden war ausreichend, um wesentliche Veränderungen der Gefüge und des Chemismus von Sphalerit zu ermöglichen. Eine rasche Abkühlung der Fluide führte zu einer Beendigung der effektiven In zwischen Fluid und Sphalerit erfolgen konnte.
    Notes: Summary A widespread feature of Variscan siderite-Pb-Zn-Cu vein deposits in the Rheinisches Schiefergebirge, Germany, is an overprinting brought about by late-Variscan Sb-rich fluids which exploited the existing vein geometry. In a number of cases, this later event led to considerable textural modification of the primary sulphide assemblage. Sphalerite is a major component of the primary mineralization in the Stahlberg (Müsen), Schöne Freundschaft (Obersdorf) and Silberwiese (Oberlahr) deposits, Siegerland-Wied district and the Silbersand (Mayen) and Saarsegen (Altenahr) deposits in the Eastern Eifel. Primary sphalerite (sphalerite 1) displays corrosion, replacement by a range of Pb-Sbsulphosalts, partial dissolution and, ultimately, remobilization as a result of the overprinting event. Remobilized sphalerite has recrystallized (Sphalerite II) directly from the overprinting fluid. A comparable textural evolution is also noted in samples from the Dörnberg-Aurora (Ramsbeck) mine, although, in this case, several distinct stages of textural modification and remobilization are recognised, resulting from a yet more complex sequence of vein emplacement. Microanalysis of sphalerite representing distinct stages of textural evolution in each of the deposits reveals extensive removal of Fe by diffusion ahead of the reactive replacement front. Second generation sphalerite contains only low contents of Fe. The data are consistent with theoretical predictions and experimental observations of interdiffusion of Fe and Zn in sphalerite in contact with a low Fe/Zn fluid. Interaction with the Sb-rich fluids was sufficiently prolonged to permit substantial textural and compositional modification of the primary sphalerite, particularly in the case of smaller grains close to the reaction front. However, relatively rapid cooling resulted in a cessation of interdiffusion before equilibrium between fluid and solid could be established.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01164152
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  • 8
    Electronic Resource
    Electronic Resource
    Late-Variscan antimony mineralisation in the Rheinisches Schiefergebirge, NW Germany: evidence for stibnite precipitation by drastic cooling of high-temperature fluid systems (2000)
    Springer
    Mineralium deposita 35 (2000), S. 206-222 
    Details
    ISSN: 1432-1866
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Antimony-rich vein mineralisation is widespread in the German part of the Variscan orogenic belt. Mineralogical investigation of a representative suite of these deposits, coupled with fluid inclusion characterisation and microthermometry, permits a reconstruction of their genetic evolution. Two structural settings host antimony mineralisation: the cores or flanks of anticlinal zones and major lithological contrasts. Channelled migration of geothermal fluids through permeable rock sequences and later stagnation of fluids in cap-rock situations inside the anticlinal zones led to mineral deposition. The mineralising event is interpreted as relating to input of deep-sourced fluids during late-orogenic exhumation at the transitional stage between collision tectonics and the late-Variscan extensional regime. Fluid inclusion data, chlorite geothermometry and the presence of meneghinite as a characteristic Pb-Sb-sulfosalt mineral in a number of vein systems allows constraints on model P-T conditions at the onset of mineralisation to be made. These are as high as 390 to 440 °C at 0.6–1.0 kbar for the Saarsegen, Apollo and Schöne Freundschaft deposits, with lower temperatures of 320–340 °C being obtained for the Spes deposit. The fluid inclusion data indicate drastic fluid cooling during the mineralising event; minimum temperatures of approximately 150–220 °C are obtained for all deposits at the end of vein quartz formation, which coincided with deposition of stibnite and most of the Pb-Sb sulfosalts. Besides the formation of extensional quartz-stibnite-Pb-sulfosalt veins, the mineralising, low-salinity NaCl-KCl-rich high-temperature tectonic brines have overprinted sulfide assemblages within earlier siderite-(Cu)-Pb-Zn veins. This has led to replacement reaction textures and remobilisation of sulfide components within the vein systems. In contrast with the earlier siderite-(Cu)-Pb-Zn veins, neither the quartz-stibnite-sulfosalt nor the (Cu)-Pb-Sb sulfosalt assemblages were affected by Variscan deformation. Rather, they display characteristic extensional features crosscutting all earlier structures and can thus be assigned to a later phase of mineralisation. Fluid composition characteristics and structural criteria indicate formation in the latest part of the Variscan mineralisation cycle; a post-Variscan genesis being rejected on grounds of conspicuously diverging fluid characteristics. A comparison of antimony deposits in the Rheinisches Schiefergebirge with other late-orogenic deposits elsewhere in the European Variscan belt indicates a significant number of shared features, enabling them to be placed into a common model related to the onset of late-Variscan brittle extensional tectonics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s001260050016
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  • 9
    Electronic Resource
    Electronic Resource
    Oxide–sulphide relationships in sodalite-bearing metasomatites of the Epembe–Swartbooisdrif Alkaline Province, north-west Namibia (2000)
    Springer
    Mineralium deposita 35 (2000), S. 430-450 
    Details
    ISSN: 1432-1866
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract The south-eastern part of Kunene Intrusive Complex (KIC), Namibia/Angola, is host to volumetrically significant, and economically important, concentrations of sodalite in the area around Swartbooisdrif, north-west Namibia. The mineralisation was formed by metasomatic exchange with carbonatites of the Epembe–Swartbooisdrif Alkaline Province. This process led to the breakdown of ore minerals initially present in various rock types of the KIC and caused the formation of new opaque phases in the sodalite-bearing metasomatites. A detailed investigation of textures and chemical compositions of the Fe–Ti oxides and sulphides has allowed evaluation of the complex ore-forming processes related to the polyphase magmatic and metasomatic history of the sodalite deposit. The predominant opaque phases in the various rock types of the KIC are ilmenite and (titano)magnetite, which are highly concentrated in the so-called magnetite plugs. It is clear from the textural evidence that most of the ilmenite and (titano)magnetite, although of orthomagmatic origin, recrystallised under subsolidus conditions. Conformably, their respective chemical compositions and phase relations represented in the system FeO–1/2Fe2O3–TiO2 point to re-equilibration at temperatures below 600 °C. Ilmenite and (titano)magnetite were affected by later deformation and decomposed by various reactions, related to, or outlasting, the metasomatic process. Oxidation of ilmenite led to the formation of symplectitic aggregates of rutile and secondary magnetite. Carbonatisation of the Fe–Ti oxides produced rutile and the siderite and rhodochrosite components in ankerite. Pyrite, in part together with rutile and secondary magnetite, was formed by sulphidation of the Fe–Ti oxides. Conspicuous aggregates of granular or lamellar intergrowths of pyrite with hematite and/or magnetite are interpreted as products of contemporaneous sulphidation and oxidation of former igneous pyrrhotite. Rarely observed pyrrhotite with pentlandite lamellae is probably not an igneous relic, but was formed during the metasomatic event. Smaller amounts of chalcopyrite, bornite, digenite–chalcocite, galena, ferroan siegenite, millerite and polydymite testify to different cooling stages during or after metasomatism. Applying the phase relations in the simplified system Fe–Co–Ni–S–O, we were able to reconstruct a semi-quantitative T–f(S2)–f(O2) path for the ore-forming processes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s001260050254
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  • 10
    Electronic Resource
    Electronic Resource
    The Askervein Hill Project: Vertical profiles of wind and turbulence (1988)
    Springer
    Boundary layer meteorology 43 (1988), S. 143-169 
    Details
    ISSN: 1573-1472
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract This is one of a series of papers on the Askervein Hill Project. It presents results from the Askervein 1982 and 1983 experiments in the form of vertical profiles of mean wind and turbulence integral statistics at upwind reference locations and at two hilltop sites. The data were obtained from a variety of sensors including sonic, Gill UVW and cup anemometers mounted on 50, 30, 17 and 10 m towers and TALA kite systems. Comparisons with numerical-model predictions are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00153977
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